Amino acid transport through the "A" system increases at an early stage of cell division or differentiation as indicated by studies in cell culture lines as well as in isolated hepatocytes and lymphocyte preparations. Recent studies suggest that this increase is due specifically to the emergence of a high affinity (HA), Na+- and energy-dependent component of the "A" system. As the emergence of the HA component is selectively suppressed by nonsteroidal anti-inflammatory drugs (NSAID) in a dose dependent manner, by a mechanism that appears to diminish the cell's ability to produce functional carriers (Vmax is decreased, without impairment of the carriers' ability to bind substrate or Na+), the possibility that this is one mechanism by which these drugs inhibit blast transformation will be investigated. Initial studies will determine whether emergence of the HA component and its inhibition by the NSAID is common to all lymphocyte populations during mitogenic stimulation. The question of whether corticosteroids have similar or more selective actions than the NSAID on this process will also be investigated. Secondly, experiments will be devised to see if emergence of the HA system is a primary event by blockade of subsequent biochemical changes during transformation (i.e., use of ornithine decarboxylase inhibitors and inhibitors of RNA/DNA synthesis) and looking at the effects of these inhibitions, if any, on amino acid transport. Lastly the possible mechanisms of the inhibition of the HA system will be sought primarily by investigation of the actions of the NSAID on thermodynamic parameters of amino acid uptake and on various aspects of cellular energy metabolism. These studies will be undertaken with freshly isolated lymphocytes from thymus and spleen, use of common mitogenic stimulants and measurement of the rate of uptake of labelled nonmetabolizable amino acids. Other parameters of blast transformation such as thymidine incorporation into cellular DNA, activation of ornithine decarboxylase and changes in cyclic AMP concentrations will be monitored.